Field of the Invention
The present invention relates to a slip control device for an electric vehicle, and relates to a technique to be able to accurately perform slip control even when a vehicle speed is in a low-speed range.
Description of Related Art
Following conventional art 1 has been proposed for an electric vehicle which performs slip control (Patent Document 1). A slip ratio λ is obtained by slip ratio estimation section on the basis of numbers of rotations N1 and N2 of a driven wheel and a drive wheel. Then, a generated torque estimation value Te due to another external force such as the vehicle body weight applied to the vehicle is obtained by a disturbance observer. An entire action torque T acting on the drive wheel is obtained by an action torque estimation section on the basis of the generated torque estimation value Te and a motor torque Tm, and a coefficient of friction μ between a road surface and a tire is estimated by a friction coefficient estimation section on the basis of this torque and the slip ratio λ. A permissible maximum torque Tmax is obtained on the basis of this coefficient of friction μ and a vertical load FZ, and torque limitation is performed such that the torque does not exceed the permissible maximum torque Tmax.
In other conventional art 2, a drive wheel maximum number of rotations is calculated on the basis of the number of rotations N1 of a driven wheel and an ideal slip ratio (λ=0.15). Torque control is performed such that the number of rotations of a rear wheel actually does not exceed this calculated maximum number of rotations. Furthermore, in order to improve riding comfort, before the number of rotations of the drive wheel reaches the maximum number of rotations, a watch range number of rotations that is set so as to be lower than this maximum number of rotations is provided. If the number of rotations of the drive wheel falls within the watch range number of rotations, torque change when the number of rotations of the drive wheel reaches the maximum number of rotations is reduced by sequentially (gradually) decreasing the torque, thereby reducing shock of a vehicle body (JP Laid-open Patent Publication No. 2014-236591).